Validating the result of a quantified Boolean formula (QBF) solver: theory and practice

Despite the increasing use of QBF solvers, current QBF solvers do not provide for any mechanism to verify their results. This paper demonstrates a methodology for independently validating the results of a DLL based QBF solver using the traces generated during the solving process. It also presents a mechanism to extract small unsatisfiable subformulas, called cores, from unsatisfiable QBF instances.